Finger joint movement sensitivity of non-cutaneous mechanoreceptor afferents in the human radial nerve.
The responses of non-cutaneous receptors in the human hand to normal digit movements were studied using single afferent recordings from the radial nerve. Eight joint-related afferents had thresholds of 50 mN or less. All responded to passive flexion movements within the physiological range of joint rotation and showed predominantly static response sensitivity; none increased its discharge during passive extension. However, only two of these eight afferents showed the same response pattern during active movements; three discharged only during the extension phase whereas the other three discharged both during extension and flexion. No high-threshold, joint-related mechanoreceptive afferents were encountered in a population of 148 afferents recorded from the cutaneous portion of the radial nerve indicating a scarcity of such afferents on the dorsal aspect of finger joints. Seven high-threshold, subcutaneous mechanoreceptive units not related to joints had thresholds for indentations of 50 mN or more and lacked responses to finger movements. Low-threshold mechanoreceptive afferents related to joints in the human hand may thus provide kinematic information in the physiological mid-range of both passive and active movements. Joint position cannot, however, be derived unambiguously from their discharge since the receptor responses may be dramatically altered by muscle activity.
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Waisman Center on Mental Retardation and Human Development, University of Wisconsin, Madison 53705-2280.
D000328:Adult; D003463:Cues; D005260:Female; D005384:Finger Joint / Q000294:innervation* / Q000502:physiology; D006801:Humans; D007699:Kinesthesis / Q000502:physiology; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D011826:Radial Nerve / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology